This invention relates to turbocharger systems for use with combustion engines. More specifically, this invention relates to a turbocharger system including hydraulic assist apparatus and method for supplementally driving the turbocharger at predetermined engine operating conditions.
Turbochargers and turbocharger systems are well known in the art, and typically comprise a turbine wheel and a compressor wheel mounted on a common shaft. The turbine wheel and the compressor wheel are mounted within isolated turbine and compressor housings, which in turn are mounted on a so-called center housing including shaft bearings and lubricant circulation passages. The turbine housing includes a gas inlet and a gas outlet, and is coupled to a combustion engine for passage of engine exhaust gases for rotatably driving the turbine wheel. The rotating turbine wheel correspondingly drives the compressor wheel which compresses ambient air and supplies the compressed air, commonly referred to as a charge air, to the engine.
Turbocharged engines are highly advantageous when compared with conventional naturally aspirated engines in that substantially denser air is delivered to the combustion chamber or cylinders of the engine. This increased air density results in an increased mass flow of available air for combustion to enable the engine to operate at substantially higher performance levels and with greater efficiency. However, an inherent limitation with turbochargers has been their inability to provide to the engine sufficient charge air during some conditions of engine operation. For example, charge air supplied to the engine by the turbocharger during low speed, full load conditions, or during low speed, acceleration conditions typically is insufficient to maintain desired engine performance levels. This inadequate flow of charge air is caused by a relatively low available energy level of engine exhaust gases to drive the turbocharger turbine wheel which in turn drives the turbocharger compressor wheel.
A variety of system concepts are known in the prior art for boosting or supplementing the normal charge air output of a turbocharger during certain engine operating conditions. Some of these concepts relate to auxiliary combustion systems for controllably supplementing the energy level of the exhaust gases with additional combustion energy to supplement driving of the turbocharger. See U.S. Pat. No. 3,988,894 for one example of this type of system. Other system concepts include multiple turbocharger turbine and/or compressor components coupled together, such as those shown by U.S. Pat. Nos. 2,173,595; 2,898,731; 3,005,306; 3,498,052; and 3,355,877. Turbocharger arrangements with supplemental mechanical drives are shown by U.S. Pat. Nos. 2,386,096; 2,578,028; 2,585,029; and 2,585,968, whereas supplemental hydraulic drives are disclosed by U.S. Pat. No. 3,389,554; 3,473,322; 3,921,403; 3,927,530; and 4,083,198. While all of these various system concepts provide at least some supplemental driving of a turbocharger, the relative expense and complexity of these systems has provided a significant obstacle to commercial application. Moreover, mechanically driven and hydraulic motor-driven systems include inherent maximum speed limitations which prevent their use with modern turbochargers including high speed components designed for rotational speeds on the order of about 100,000 R.P.M. or more.
Some prior art system concepts include hydraulic turbines for driving a centrifugal compressor to supply charge air to an engine. In some designs, the hydraulic turbine is embodied in a supercharger system, as in U.S. Pat. No. 3,036,563. In other designs, the system proposes an hydraulic turbine for supplementally driving the turbocharger as through a direct connection to the turbocharger shaft. See U.S. Pat. Nos. 2,968,914; and 3,869,866; and British Pat. No. 488,396. However, these prior art hydraulic turbine systems have included so-called Pelton-type turbine wheels requiring a ventilated chamber for operation. Accordingly, any attempt to operate the Pelton turbine wheels at relatively high rotational speeds results in generation of large quantities of a foamy mixture of air and hydraulic fluid which must be dissipated before recirculation to the turbine wheel or to other system components. This is particularly disadvantageous when the hydraulic fluid is shared with another fluid system, such as an engine lubrication system, in that the foamy mixture does not return rapidly to liquid state, and cannot be used or pumped in foam form for use in the shared fluid system. Moreover, even when free-wheeling with the turbocharger, Pelton-type turbine wheels are not capable of withstanding the high rotational speeds achieved by modern turbochargers. As a result, Pelton-type hydraulic turbine systems have not found commercial application in modern high speed turbocharger environments.
This invention overcomes the problems and disadvantages of the prior art by providing a turbocharger system specially adapted to include a nonventilated hydraulic turbine driven by an hydraulic fluid shared from another hydraulic system for controllably and supplementally driving a turbocharger.